Step-by-step installation tips

Masonry Construction, March, 2006

1. Around the Bend

Most manufactured stone packages include L-shaped pieces that wrap around outside corners. One leg of the stone is typically shorter, allowing an alternating pattern up the wall. The most important preparation detail is to continue the mesh tightly around corners in one piece, rather than breaking the seams at the corner. Some contractors install a galvanized metal corner strip to keep corners straight and firm.

2. Scratch until hard

The first step in preparing for good adhesion is to apply an even scratch coat of mortar and allow it to dry. Many installers take an extra step that may not be prescribed in the installation guidelines of the stone makers. They add an additional brown coat to increase hardness whenever the backing for the metal lath is not solid; for example, over rigid foam or bare studs with a paper-backed lath.

3. Cut or break

Different stone types affect the method of cutting or trimming. Cultured Stone's River Rock can be banged apart with a trowel. Many drystack stones can be cut with a diamond blade using a circular saw. To minimize cutting, consider interlocking stones, and start the wall from either the top or the bottom (not in the middle) so you only cut one row. For rougher stone types, a hatchet can trim off distressed-looking chunks, or use wide-mouth nippers, similar to those for tile work.

4. Slap it on

Most masons recommend applying mortar directly to the back of each stone, rather than simply depending on a coat of mortar on the wall surface. The thickness of the mortar should be between 1/2 inch and inch. For larger stones, apply mortar in the pattern shown. Be sure the water mix is not too wet to avoid slippage. Stones should be pushed and wiggled into the wall surface hard enough for some mortar to squeeze out around the edges. Rules about joint width vary between stone types, but in general the average should not exceed 3/4 inch. If this is a drystack stone, the mortar color is the grout color. Choose carefully.

5. Grout it out

With grouted stone styles, match the grout color to the darkest color in your stone of choice, and fill a grout bag (like a big pastry bag) with the chosen mix. Squeeze the mixture into gaps. Try not to get mortar on the surface of the stones because it is hard to remove. Cultured Stone suggests that if you do get mortar on the stones, remove it later when it is partially dry, using a whisk broom, not a wire brush.

6. Tuck and shape

Grout finishing is often the most labor-intensive part of a stone installation. If using a traditional recessed grout line, point the joints with a stick or pointing tool when the grout is firm. The Tuscan style of grout has become very popular, at least in California. In this look, grout overlaps the joint by as much as 1/2 inch. To create this look, apply extra grout to begin with, and smooth it with a damp sponge. Later, go back with a wire brush and shape the grout to the client's pleasure.

Below the Belt

The toughest transition point when working with any manufactured stone can be where the framing ends and the foundation begins. Resist any temptation to run the stone all the way to grade, because doing so can cause the manufactured stone to stain or oxidize. To create a clean line at the wall's base, build a short jig from 2 x 4 lumber, as shown, that can be staked into the ground and leveled. The transition can be flashed at the base of the wall the same way you would with stucco. See the manufacturer's installation guide.